The rise in fuel costs and the impact of global warming due to increase in carbon dioxide emissions have led to renewed interest in renewable energy, primarily wind and solar. Although wind energy technology has developed considerably, it still faces major challenges that prevent it from competing with fossil fuels. One of the problems facing the wind turbine industry is the reliability of wind turbine drivetrains. Research conducted at University of Minnesota aims to improve the reliability of wind turbine drivetrain by replacing the conventional drivetrain with a Hydrostatic Transmission (HST). HST is a reliable, robust and a mature technology that has been used in demanding application since more than half a century. An HST system also enables robust energy management features like energy regeneration using hydraulic accumulators.
The goal of this thesis is to explore short term wind energy storage to improve the energy captured by a wind turbine by using an HST coupled to a hydraulic accumulator. Mathematical models of the wind turbine and the HST system is developed to understand its dynamics and to validate the energy storage ideas via simulations. The characteristics of wind are investigated to understand the nature of wind and explore opportunities for energy storage. A novel method for capturing more energy from the wind is proposed. Control strategies are developed and accumulator storage system configurations are proposed to achieve the storage objectives.
The performance of the control strategies and accumulator storage configurations are simulated in MATLAB/Simulink environment. Results show that a 50 kW turbine using an energy storage system and located at a high turbulence site can increase the Annual Energy Production (AEP) by more than 4% using a 60 liter hydraulic accumulator.

Dutta, Rahul.
(2012).
Modeling and Analysis of short term energy storage for mid-size hydrostatic wind turbine.
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